The Portland Thorns are one of the youngest teams in America's youngest sports league. But after little more than two years of existence, one of their players decided to retire.

Nikki Marshall, a 26 year-old a defender, announced in February that she was retiring from the Thorns and the National Women's Soccer League (NWSL). Ms. Marshall, who started the first 46 regular season games in the Thorns' history over the past two years, cited low pay as one of the main contributors to her decision.

Retiring at 26 would be something close to financial suicide for a male professional soccer player. At that age, players are generally entering their athletic prime and can make millions of dollars a year. The average player salaries in Europe's top four leagues – the English Premier League, the German Bundesliga, Italy's Serie A, and Spain's La Liga – sits at just over £1.5 million (around $2.3 million) a year, or about £30,000 ($47,000) a week, according to The Daily Mail.

In contrast, players in the NWSL make between $7,000 and $38,000 each season. Many of them have to work second jobs in order to make ends meet. Marshall supplemented her income by working in a part-time sales job at Avnet Technology, the Oregonian reported. Other Thorns players have balanced semi-professional soccer with part-time jobs and night shifts.

"I don't think people realize the lifestyle we live when we play," Marshall told the Oregonian. "Most everybody has a second job."

Still, women's soccer players in the US probably have it better than players in other leagues around the world. The US, Canadian, and Mexican women's soccer federations pay the salaries of the players they allocate to the NWSL – about 40 of the league's roughly 190 players – and some of the more high-profile players in the league can supplement their salaries with endorsement deals. US star Alex Morgan is the top earner, making almost $3 million a year, but about $2.8 million of that comes from endorsements, according to the BBC, including deals with Nike, Panasonic, and Coca Cola.

The majority of NWSL players who aren't paid by their national federations are seeing their wages limited by a $265,000 salary cap on teams – it is the third such league to form in the US in the past 13 years, with others folding due to financial difficulties – and league officials are hoping that as the league grows sustainably, player salaries will grow with it.

Jeff Plush, the NWSL commissioner, says in an email to the Monitor that the league is "exactly where we projected to be at this point in time" after two and a half years in business. The league is seeing growth in ticket sales and sponsorship sales, he added, and is "very close" to announcing a new national TV deal for this season. He says the league want to expand from nine teams to ten "in the near future," and eventually grow to a 12-team league over the next five years.

Mr. Plush also says that the salary cap structure, with minimum and maximum salaries, is reviewed after every season.

"We have raised the minimum and maximum salaries as well as the salary cap each season, and expect that to continue in the future," adds Plush. "There is always more that can be done, but the momentum and excitement is exploding around the women’s game and soccer is truly growing in North America."

Unlike the men's game, women's soccer in Europe is actually being outpaced by its US competition, both in terms of player wages and the quality of the soccer.

Europe has its share of star players, including Marta, the five-time FIFA women's player of the year. Now playing for Rosengard in the Swedish league, the Brazilian reportedly earned $400,000 a year from her previous club Tyreso, also in the Swedish league.

But as in America, the financial reality for the majority of players is that of juggling soccer with other part-time jobs, or putting other careers on hold. The Women's Super League in England has been operating since 2011 and, like the NWSL, players on the British national team are awarded central contracts worth up to £26,000 a year. Some players can even earn up to £65,000 a year. But Matthew Buck, an agent with the Professional Footballers' Association, told the BBC that only a small number of players make that much.

"There are players in the WSL who are on as little as £50 a week," said Mr. Buck.

In terms of revenue and player endorsements, the WSL is decades behind. While WSL attendance has reached record levels this year – with an average of 892 fans per game, according to the BBC – the league is far behind the NWSL, where attendance averaged over 4,000 last year.

Eniola Aluko, a striker for England and Chelsea in the WSL, told the BBC that while salaries have improved in the English league, she'd like to see salaries reach the level of those in the US.

"Hopefully we can get to that point," said Ms. Aluko, who put her career as a lawyer on hold to pursue a soccer career. "But it's great to see role models like [US stars] Abby Wambach or Alex Morgan earn a lot of money but also respect playing for their country."

But perhaps the bigger challenge is ensuring that women's players who can't attract endorsements and national team salaries can also make soccer a full-time profession. The Thorns had the greatest average attendance in the NWSL by far last year, at over 13,000 fans a game, but the team still couldn't pay Nikki Marshall enough to stay in the game.

"It's a wonderful life and you do it as long as you can because you love it," Marshall told the Oregonian. "But, as female athletes, we don't necessarily get the same respect as male athletes or the respect that we deserve. It's not an easy life."